Self-Propelled Nano/Micromotors with a Chemical Reaction: Underlying Physics and Strategies of Motion Control

TLDR

Nano/micromotors with regulated motions are common in nature, yet their application in man-made chemical systems is unexplored; their physics differs from macroscale motors, dominated by viscous forces and thermal fluctuations, and the field remains at a fundamental stage requiring further research. This review examines artificial nano/micromotors proposed over the last decade, focusing on chemically propelled motors—catalytic and self-reacted—since most biomotors consume chemical energy. The review discusses fabrication of motors that overcome viscous forces via various mechanisms, including catalytic and self-reacted chemical propulsion, and explores directional control through chemotaxis, external fields, and confinement. We expect that chemical systems mimicking elegant biological ones will be realized in the near future.

Abstract

Nano/micromotors exhibiting regulated motions are ubiquitous in nature, with biological ones having highly sophisticated and functional properties. However, nano/micromotors have not been applied in the design of useful man-made chemical systems to our knowledge. In this article, we review artificial nano/micromotors that have been proposed in the last decade. The underlying physics is completely different from that of conventional macroscale motors. The viscous force dominates the regulated motion of a nano/micromotor, in which thermal fluctuation converts into active Brownian motion. To overcome the viscous force and sustain motion, motors driven by various types of mechanisms have been fabricated. We focus on chemical reaction propelled motors classified into catalytic and self-reacted ones because most biomotors move by consuming chemical energy. Furthermore, the directional control of artificial nano/micromotors by chemotaxis, external field, and confined space is also discussed. As this hot and challenging topic is still currently at a fundamental stage, practical research will be required for developing various applications. We expect that chemical systems mimicking elegant biological ones will be realized in the near future.